Spontaneous and evoked otoacoustic emissions (SOAEs and EOAEs), of apparent cochlear origin, in the ear canals of human subjects constitute and extremely valuable non-invasive probe of the active nonlinear response of the cochlea which determines detection and processing of low level signals. The generation mechanisms of these emissions may be reversibly manipulated by means of external tones and/or noise (either ipsilateral or contralateral), and by the intake of aspirin. The knowledge of auditory function obtainable from measurements of spontaneous and evoked otoacoustic emissions and associated psychoacoustic measures (detection and discrimination), may be greatly enhanced if measures of all these phenomena can be obtained from individual subjects during such manipulation. To this end comprehensive data on otoacoustic emissions and related psycho-acoustical measures will be obtained from subjects with a variety of emission patterns and the data will be compared with the predictions of cochlear models incorporating both active and nonlinear mechanisms based on recent models incorporating both active and nonlinear mechanisms based on recent research into cochlear processes.